(a) Field of the Invention
The present invention relates to a method of manufacturing a cathode ray tube (CRT) and a heating device for use in the CRT manufacture and, more particularly, to a method of forming a frit seal between a stem and neck of the CRT, minimizing defects of the CRT such as oxidization of an electron gun and stem pins, deterioration in the electron emission efficiency, shortage in the life span and occurrence of a crack of the CRT.
(b) Description of the Related Art
Generally, CRTs are designed to reproduce the original picture image on a screen through receiving the picture image signals from the external and exciting phosphors coated on the screen with electron beams in accordance with the signals. The CRT usually includes a panel having an inner surface coated with phosphors, a funnel sealed to the panel in a vacuum-tight manner, and a neck sealed to the rear of the funnel to accommodate an electron gun therein.
The electron gun is mounted on a stem to receive currents for emitting, focusing and accelerating thermal electrons therefrom. The stem is fitted into the neck and firmly sealed to it.
FIG. 8 shows a sealing state of the stem S to the neck N according to a prior art. The stem S is first inserted into the neck N. Then, the outer surface of the neck N adjacent to the flange of the stem S is fused to form a seal therebetween and the remaining end portion of the neck N is removed.
However, when the end portion of the neck N is cut off or drops to be broken to pieces, fine glass powder is generated.
The glass powder wanders through the factory and intrudes into the inside of the CRT through the exhaust pipe externally attached to the stem or through the opening portion of the neck before the sealing operation. As a result, it clogs beam-guide holes formed on a shadow mask of the CRT. This causes a serious defect in the CRT. Furthermore, since the remaining end portion of the neck is cut off and waste-disposed after the sealing operation, a minus effect is resulted in the production costs.
Another conventional method of sealing the stem to the neck is disclosed in a Japanese Patent Laid Open No. 8-83582. In the method, a bottom end of the neck is positioned on an upper portion of the flange of the stem and fused to form a seal therebetween.
However, there is a gap between the bottom end of the neck and the upper portion of the flange because they do not practically make a uniform contact side. And when the fusing operation is performed onto the gapped contact side by a heating device such as a torch, the torch flame penetrates into the inside of the neck through the gap. As a result, the electrodes of the electron gun and the stem pins are oxidized so that the electron emission efficiency is deteriorated. Furthermore, the temperature of the torch flame is extremely high and, hence, a distortion defect is generated in the neck glass, causing a crack.